Acrobeles dimorphus Heyns & Hogewind, 1969

Boström, Sven & Holovachov, Oleksandr, 2019, Descriptions of species of Acrobeles von Linstow, 1877 (Nematoda, Rhabditida, Cephalobidae) from Kelso Dunes, Mojave National Preserve, California, USA, Zootaxa 4651 (2), pp. 330-350 : 341-344

Acrobeles dimorphus Heyns & Hogewind, 1969

( Figs 11–13 , Table 3 )

Material examined. One female and two males on slides # SMNH-149105–SMNH-149106 deposited in the invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Locality and habitat: USA, California, Mojave National Preserve, Kelso Dunes , soil around roots of desert plants (N 34 53.698’, W 115 42.155’), 28 March 2010, legit O. Holovachov & P. De Ley.

Description. Adult. Body strongly arcuate ventrad when killed by heat. Cuticle “double”, coarsely annulated, annuli 2.0– 2.7 µm wide at midbody and 2.0– 2.4 µm in pharyngeal region. Lateral field with two incisures (one wing); extending to phasmid in both sexes; occupying about one-fifth of midbody diameter. Lip region slightly offset, carrying six labial and four cephalic papillae and two small, rounded amphid openings. Six triangular lips arranged in three pairs, one dorsal and two ventrolateral. Pairs of lips separated by primary axils with two triangular-elongate guarding processes originating from the incomplete first annulus. Secondary axils separating the lips of the pair also with two triangular-elongate guarding processes but separate from the first annulus. Each lip asym- metrically triangular, with about 13–15 tines along its margin: 6–7 short tines and one longer apical tine facing the primary axil, 6–7 short tines and one long tine in the middle facing the secondary axil. Three labial probolae 12 µm high, deeply bifurcate into two prongs having an outer margin with 7–8 tines, an inner margin with 6–7 tines and two longer apical tines directed forward. Stoma length about one time lip region diameter. Stomatal parts less well discernible. Cheilorhabdia rounded in median section; metastegostom with a dorsal denticle. Pharyngeal corpus cylindrical-fusiform with wide lumen; isthmus narrow, demarcated from corpus by a break in muscular tissue; bulb oval with valves. Cardia enveloped by intestinal tissue. Nerve ring and excretory pore at level of metacorpus. Dei- rids at level of metacorpus-isthmus junction to isthmus.

Female. Reproductive system monodelphic, prodelphic, in a dextral position in relation to intestine. Ovary reflexed posteriorly at oviduct, with a double flexure posterior to vulva. Spermatheca and postvulval uterine sac well developed. Vulval lips not protruding. Phasmids located at about one-fifth of tail length. Tail conoid-elongate with about 25 ventral annuli, tail terminus pointed.

Male. Reproductive system monorchic, dextral in position; testis reflexed ventrad anteriorly. Spicules paired and symmetrical, curved ventrad; with oval manubrium and subcylindrical, gradually narrowing shaft. Gubernaculum plate-like. Genital papillae distributed as follows: three ventrosublateral precloacal pairs at 6–10 µm, at 24–29 µm and at 53–60 µm anterior to cloaca; a single midventral papilla on anterior cloacal lip; two pairs (one subventral and one lateral pair) at mid-tail; three pairs (one subdorsal, one subventral and one lateral pair) near tail terminus. Phasmids located at about two-fifths of tail length. Tail strongly curved ventrad, conoid, with a short, rounded mucro.

Diagnosis (supplemented with literature data). Acrobeles dimorphus is characterised by a 541–890 µm long body in females and 494–830 µm in males; cuticle coarsely annulated; lateral field with two incisures (one wing), extending to phasmid in both sexes; six triangular lips arranged in three pairs; pairs of lips separated by primary axils with two triangular-elongate guarding processes; secondary axils separating the lips of the pair with two triangular-elongate guarding processes; each lip asymmetrically triangular, with about 13–15 tines along its margin: 6–7 short tines facing the primary axil, 6–7 short tines facing the secondary axil and two longer apical tines; three labial probolae, deeply bifurcate into two prongs having an outer margin with 7–8 tines, an inner margin with 6–7 tines and two longer apical tines directed forward; pharyngeal corpus 3.1–4.0 times isthmus length; nerve ring at level of metacorpus-isthmus junction; excretory pore and deirids at level of isthmus; spermatheca 37 µm long; postvulval uterine sac 1.5–2.0 times vulval body diameter; spicules 33–35 µm long.

Remarks. The specimens of Acrobeles dimorphus collected from the Kelso Dunes area and described here agree in many respects with the type specimens described from Namibia by Heyns and Hogewind (1969). One major difference is the much shorter body length (541 µm in females and 494–573 µm in males vs 830–890 µm in females and 760–830 µm in males in the type population). However, they agree in size with some smaller specimens recorded from the type locality by Heyns and Hogewind (1969) and identified as A. dimorphus (female 580 µm, male 520–540 µm, see Table 3 ).

Figures

FIGURE 11. Acrobeles dimorphus Heyns & Hogewind, 1969. A. Pharyngeal region. B. Female gonad. C. Female tail. D. Male tail. Scale bar=20 µm.

FIGURE 12. Acrobeles dimorphus Heyns & Hogewind, 1969, photomicrographs. A-B. Labial region of a male at different focus levels. C. Lateral field along pharyngeal region of a male (arrow indicates deirid). D. Lateral field at midbody of a female. Scale bar=20 µm.

FIGURE 13. Acrobeles dimorphus Heyns & Hogewind, 1969, photomicrographs. A. Female gonad. B. Anterior part of male gonad showing ventrally flexed testis. C. Tail, median section showing gubernaculum. D. Tail, submedian section showing spicule. E. Tail, surface view (arrows indicate precloacal papillae). Scale bar=20 µm.